This invention relates to the field of ventilation. More particularly, an airflow device, such as a fan, is provided with an automatic failure mode to place the device in a configuration to either impede or allow airflow.
Multiple fans or similar airflow-inducing devices (e.g., blowers) are often used together to increase the volume, rate or force of ventilation. For example, two or more small axial fans may be used in parallel or in series to generate airflow through a computer system or other piece of electronic equipment. In a parallel arrangement, the fans promote parallels flows of air through different apertures or openings in the equipment. In a series configuration, the fans are aligned in sequence from a single aperture.
When one fan in a multi-fan arrangement fails, its failure can significantly affect the operating efficiency of the other fan(s). In a parallel arrangement, when one fan fails, it may create a xe2x80x9cshort-circuitxe2x80x9d that prevents air from flowing through much of the equipment. In a series configuration, the blades of the failed fan will impede the airflow generated by the remaining fan(s).
Attempts to alleviate the impact of a fan failure on a functioning fan have been ineffective or have caused other problems. For example, a baffle or flap may be added to a fan operating in a parallel configuration. The baffle is blown out of the way when the fan is operating, but is intended to block the fan if it fails. However, even if the baffle helps block the fan when it fails, while the fan is operating, some of the efficiency of the fan is wasted on keeping the baffle open. In addition, the baffle occupies space that may be put to better use.
In a series arrangement, a fan may be equipped with fewer blades so that it creates less impedance if it fails. However, the decreased number of blades affects the fan""s efficiency when it is operating.
Therefore, there is a need for an airflow device (e.g., fan, blower) that can automatically fail into a mode or configuration that either blocks or opens an air channel through the fan, as desired.
In one embodiment of the invention, an airflow apparatus (e.g., a fan, a blower) is provided for impeding or facilitating airflow through a channel when the apparatus fails or is inoperative. The apparatus comprises a set of blades or airfoils that, when operating, promote or force a flow of air through the channel. The apparatus also includes a bias mechanism for biasing the blades of the apparatus toward failure positions blocking or opening the channel when the apparatus is at rest or turned off. When the apparatus begins spinning, the bias mechanism is overcome and the blades take their normal operating positions. The apparatus may be employed by itself or as one of multiple apparatuses working together.
In different embodiments, the bias mechanism may comprise a spring or elastic material that resists rotation, extension or other type of blade transition from the failure position to the operating position or promotes rotation, contraction or other transition from the operating position to the failure position. In one implementation, the bias mechanism may involve a blade design (e.g., weighting) that attempts to place a blade in its failure position by the force of gravity. In these embodiments, and others, centrifugal force generated by the spinning blades places the blades into their normal operating positions. However, when that centrifugal force is terminated or sufficiently attenuated, the blades are returned to their failure positions.